Matlab coder generated a c function which has void output, even though the matlab function has double array input

My matlab function is of the following form =

function Y = fn(X) 
%some code here
end

where both X and Y are vectors of type double

I used Matlab coder to convert this into a c program function.

The c file is of the form -

void fn(X,Y){
//stuff goes here
}

But I want the function to return Y. (I assume in this format, I have to send the pointer of output as the input argument).

How to I change this?

Answer 1

[Darshan Ramakant Bhat]

This is an intentional design in the generated code and the users dont have control over it to change this behaviour as of today.

Reason for the design :

In the current design, the caller function will need to create the pointer (memory) and owns it. Memory creating and the deletiong is done in the same function.

int main {

// Allocate input and output memory
int *input = (int*)(calloc(10,sizeof(int)));
int *output = (int*)calloc(10,sizeof(int)));
for (i =0;i<10;++i) {
        // Fill the input
        input[i] = i;
    }
// Use the generated code

foo(input,output);

// Do something

//Destroy the memory
free(input);
free(output);
    
}

If you return the pointer as output, that pointer needs to be created inside the function, so the ownership of the memory is not clear.

int* foo(int *input) {
// does something

// Allocates the memory
int *out = (int *)(calloc(numel,sizeof(int)); // Who owns this memory ? this may be leaked. 
                              
return out; // Also the size information is lost due to array decaying into pointer. 

}

The generated code contains an example main.c file which shows a sample use of the generated function. You can take a look at it :

https://www.mathworks.com/help/coder/ug/generate-and-modify-an-example-cc-main-function.html#buod5pb

Hope this will help you.